Means and method for electroacoustic transducer excitation

Abstract

The invention relates to ultrasonic welding methods and apparatus for correcting the difference of frequency and phase of transducer mechanical oscillations and oscillator driving impulses to the transducer under conditions of discontinuous loading, thereby to increase the efficiency of the transducer excitation. The transducer excitation impulses are periodically supplied to the transducer at a length not more than a half-period of the transducer mechanical oscillations, and after termination are resumed again with adjustment phase and frequency determined by transducer striction feedback signals. A zero-crossing detector applies the resumed and adjusted phase and frequency driving impulses, thereby corresponding to the highest transducer sensitivity. Feedback impulses established by the transducer mechanical resonance characteristics under varying load control the phase and frequency of the excitation pulses.

What is claimed is:  
     
       1. A method of driving a loaded electroacoustic transducer at discontinuous intervals with electric excitation impulses supplied to the transducer at one of a determined resonant frequency or frequency multiple thereof to induce mechanical oscillations of the transducer for impacting a work interface presenting variable loading factors while confining duration of said impulses to not more than half a period of said mechanical oscillations, wherein the excitation impulses are discontinuously interrupted while the transducer is impacting said work interface, comprising the steps of: 
       attaining a feedback voltage from the driven transducer when impacting said work interface representative of the displacement of the transducer and its intrinsic mechanical oscillation frequency and phase,  
       resuming the excitation impulses after interruptions at a phase corresponding to the highest loaded transducer sensitivity providing for maximum values of ultrasonic displacement amplitude at varying loads, and  
       adjusting the oscillator frequency and phase at the resumption of the excitation impulses to match the frequency and phase exhibited by the intrinsic mechanical oscillation frequency of the driven transducer at the resumption time.  
     
     
       2. The method of claim  1  further comprising the step of terminating the excitation impulses at a zero-crossing point of the transducer oscillation frequency. 
     
     
       3. The method of claim  1  further comprising the step of periodically terminating the excitation impulses. 
     
     
       4. A system of driving a loaded electroacoustic transducer at discontinuous intervals with electric excitation impulses supplied to the transducer at one of a determined resonant frequency or frequency multiple thereof to induce mechanical oscillations of the transducer for impacting a work interface presenting variable loading factors while confining duration of said impulses to not more than half a period of said mechanical oscillations, wherein the excitation impulses are discontinuously interrupted while the transducer is impacting said work interface, comprising: 
       means for attaining a feedback voltage from the driven transducer when impacting said work interface representative of the displacement of the transducer and its intrinsic mechanical oscillation frequency and phase,  
       an oscillator for timing the excitation impulses,  
       control means for interrupting the excitation impulses and resuming the excitation impulses after interruptions at a phase corresponding to the highest loaded transducer sensitivity providing for maximum values of ultrasonic displacement amplitude at varying loads, and  
       means for adjusting the oscillator frequency and phase at the resumption of the excitation impulses to match the frequency and phase exhibited by the intrinsic mechanical oscillation frequency of the driven transducer at the resumption time.  
     
     
       5. The system of claim  4  further comprising means for terminating the excitation impulses at a zero-crossing point of the transducer oscillating frequency. 
     
     
       6. The system of claim  4  further comprising means for periodically terminating the excitation impulses.